1. Field of the Invention
The present invention relates to a piezoelectric ink jet printer head and a method for manufacturing the same.
2. Description of the Related Art
FIG. 1 shows a conventional ink jet printer head 100 used in an ink jet printer. The ink jet printer head 100 includes a cavity plate 130 and a piezoelectric actuator 110. The cavity plate 130 is formed with a plurality of ink chambers 131. The piezoelectric actuator 110 is adhered onto the cavity plate 130 so as to cover the ink chambers 131. When a voltage is applied to the piezoelectric actuator 110, the piezoelectric actuator 110 deforms into the ink chambers 131, whereupon the volume of the ink chambers 131 decreases. As a result, the pressure in the ink chambers 131 increases so that an ink droplet is ejected from the orifices 132 of the ink chambers 131.
The piezoelectric actuator 110 includes active layers 120 and inactive binding layers 150. The active layers 120 include piezoelectric ceramic layers 140 that are formed with an internal negative electrode layer 142, laminated in alternation with piezoelectric ceramic layers 140 that are formed with internal positive electrode layers 144a, 144b, and 144c. The internal positive electrode layers 144a, 144b, and 144c are aligned with the ink chambers 131 of the cavity plate 130. The binding layers 150 includes a plurality of layers of piezoelectric ceramic layers 171 that are unrelated to drive of the ink jet printer head 100.
When a drive voltage is applied between the internal positive electrode layers 144a to 144c and the corresponding internal negative electrode layer 142, the lowermost piezoelectric ceramic layer 140, that is, the piezoelectric ceramic layer 140 adhered to the cavity place 130, is actually inactive and does not add to the drive force of the ink jet printer head 100.
However, because the lowermost piezoelectric ceramic layer 140 is inactive in this way, a sufficiently high positive pressure is not generated in the ink chambers 131. It is conceivable to screen print another electrode for driving the lowermost piezoelectric ceramic layers 140 onto the surface where the lowermost ceramic layer 140 attaches to the cavity plate 130. However, a separate insulation film would need to be formed on this electrode to protect it from the ink in the ink chambers 131. This extra film would increase production costs.
It is an objective of the present invention to overcome the above-described problems and provide a piezoelectric type ink jet printer head and a method of manufacturing a piezoelectric type ink jet printer head that enables the lowermost piezoelectric ceramic layer that is adhered to the cavity plate to be driven as an active layer.
In order to achieve the above and other objectives, there is provided an ink jet head including a cavity plate and a piezoelectric actuator. The cavity plate is formed with a plurality of nozzles and a plurality of pressure chambers in one-to-one correspondence with the nozzles. The piezoelectric actuator includes a plurality of first piezoelectric sheets and a plurality of second piezoelectric sheets laminated in alternation. Each of the first piezoelectric sheets being provided with a first electrode, and each of the second piezoelectric sheets is provided with a second electrode. One of the first piezoelectric sheets has a first surface on which the first electrode is provided and a second surface opposite from the first surface and provided with no electrode, the second surface being attached to the cavity plate while covering over the pressure chambers. The cavity plate and the second electrodes are all connected to a same potential.
There is also provided a manufacturing method for an ink jet head. The method includes the steps of forming a laminated structure of a plurality of first piezoelectric sheets and a plurality of second piezoelectric sheets laminated in alternation, each of the first piezoelectric sheets being provided with a first electrode on a first surface, each of the second piezoelectric sheets being provided with a second electrode, attaching a second surface of a lower most one of the first piezoelectric sheets to a cavity plate, the second surface being opposite from the first surface, and polarizing the first piezoelectric sheets and the second piezoelectric sheets by applying a voltage between the first electrodes and corresponding ones of second electrodes and between the first electrode on the lower most one of the first piezoelectric sheets and the cavity plate.